The ability to accurately assess correct injection dosage is most commonly associated with visual cues. For example, volumetric marks already come printed or etched on the side of conventional syringe bodies, and this remains the most common form of measurement. A practitioner injects a certain amount of a substance, such as a drug, by verifying fluid level using these volumetric marks.
Even more generally, a physician can intake an amount of a drug to be injected into the syringe using the volumetric marks. Then, a practitioner can simply expel the entire volume into a patient in a single plunger run. Such a full expulsion of drug removed the need to only inject a portion of a drug in a syringe. Thus, for pharmaceutical drugs, the benefits of injecting the correct dosage should not require explanation.
However, in applications using sensitive drugs such as botulinum toxin or aesthetic soft tissue fillers, for example, hyaluronic acid-based dermal fillers such as Juvederm® XC, manufactured by Allergan, Inc., dose indication provides the practitioner with additional control over precise facial sculpting.
Additionally, with applications like botulinum toxin, injection of multiple small, precise doses of toxin may be advantageous over injection of a large bolus of the material.
Further, with fat grafting, injection of multiple small, precise doses of fat cell-containing material may be advantageous over injection of a single large bolus of the material. Smaller bolus injection increases retention of the injected material, possibly by providing greater vascularization of the material throughout the fat cells and improving survivability thereof. Injection of a large bolus is less likely to be retained long term as the injected fat cells may be more prone to die, due to lack of vascularization, for example.
Many of these injectable materials, for example, dermal fillers and fat grafting materials, are not easily extruded through standard syringes and accompanying cannula. These materials tend to provide significant resistance to be pushed through a narrow cannula. The problem is even more exacerbated by the fact that these materials are often used for detailed precision work in facial contouring and body sculpting.
Injection devices, both manual and motorized, have been specifically developed, or at least proposed, to address these issues. Interestingly, many physicians prefer the use of manual conventional syringe injectors over electronically controlled, motorized devices. For at least this reason, there remains a need for devices (e.g., simple devices) that can be attached to a standard syringe and which provide better control over small aliquot dosing of relatively difficult to inject materials, for example, dermal fillers, fat grafting materials and the like.